This invention relates to one-way check valve assemblies, and is more particularly directed to a check valve whose seat portion can be formed of a flexible material and unitarily with a peripheral item, such as a barium enema tip.
Previous check valves for air or fluid passage typically have a ball or similar stopper and a tubular member that contains a seat. For medical or surgical uses, the seal should be as good as possible.
One type of valve construction made for high sealing (i.e., low leakage) characteristics requires that the stopper and seat be made to a high degree of accuracy. The precision of fit of the stopper in the seat determines how well the valve seals. This is easiest to achieve with all-metal valves, because steel, brass, and other metals are easily machined to the required precision, and materials are dimensionally stable. However, with this construction, these valves are quite expensive and are not considered disposable, nor can they be incorporated unitarily into a periheral device. This design of valve is unsuited for construction from molded plastic parts, especially from flexible plastic resins which by their nature are dimensionally unstable.
Another proposal involves employing a soft material for the valve seat and a ball type stopper of hard metal or glass. This reduces the requirement for precision, because the soft seat material can conform to the shape of the stopper to effect a good seal. However, because the seat material is soft, a rigid barrel is required to house the valve seat. The soft material of the seat, in order to be soft enough to conform, has to be too soft also for dimensional stability. The upshot of this is that the seat cannot simply be formed as a unitary part of a peripheral device, because the device would either be too flexible for it to function in its own role, or too rigid to serve as a flexible seat check valve. Also, if the seat is formed inside a part of a peripheral device that is made of a flexible material, then as the device itself is flexed even slightly, the seat distorts and the seal between the hard ball stopper and the seat will break.
If a soft material is used for the stopper, this also reduces the requirement for precision because the stopper can conform to the shape of the seat. In this case, the materials requirement for seat can be somewhat less critical. Nevertheless, if conventional shapes, or profiles are employed for the seat and stopper, there is a tendency for the seat to deform and break the seal even under normal operating conditions. If the seat and its enclosing barrel are not rigid, and the stopper is a spherical member, there is a risk that the seal will break, if the seal is even slightly deformed. Other forms use either a rigid seat with a flat face or a flexible seal in a rigid barrel.